Can't answer your question, but I can say that I decided the effort to remove the plug far exceeded my will to do it. I bought a Zerostart 1 1/2" lower radiator hose heater on Ebay for around $10 and spent half an hour installing it. Works fine.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13